If you have Windows 7 or later, set up a Homegroup and on the things you want to share, right click, choose share with and choose the Homegroup.
On Windows XP you need to Click Start -> type System in the box, and press <enter> This will open the system properties page.
Where it says "Computer name, domain, and workgroup settings" click "Change settings" over to the right.
On the next screen, where it says "To rename this computer ..." click the Change button on the right.
Here, where it says "Member of" select Workgroup. You can leave this at the default of Workgroup or you can name it something else. I generally prefer to name it something else, otherwise if it is a laptop for example, and you connedt at another location, all of the machines there who are a part of "WORKGROUP" will have the same access to your computer as any workgroup computers at home. In order to have access, they have to be in the same workgroup.
When you click OK you will get a message that you have to reboot before the settings will apply. Go ahead and reboot.
Logged back into your account, using Windows Explorer, navigate to whichever folders you want to share, right click, choose Sharing and enter the appropriate settings.